With their 800 mm guns, 270 mph race cars and dreams of an empire from the Atlantic to the Caspian, those Third Reich people sure had a thing for big. The Breitspurbahn (broad-gauge railway) was bigger than big: a brand new cross-continental railway with a gauge of 9 feet and 10 ⅛ inches, it was to run the length and breadth of Grossdeutschland.

To see how big a leap the Breitspurbahn was, consider that the standard rail gauge—the distance between the two rails—used in most countries is 4 feet and 8 ½ inches: less than half of Hitler’s planned ride across Europe.

Broad gauge is useful for massive rolling stock and high speeds, but it’s got a major downside: backward compatibility. Apple may discard the optical drive and the Firewire port on MacBooks with nothing worse than a few days of indignant blog posts, but railways live and die by compatibility. This is one reason why Siemens and ThyssenKrupp’s wonderful Transrapid maglev monorails have such a hard time taking off: other high speed railways that can travel at slow speed on normal rail lines will always be orders of magnitude cheaper.

The Breitspurbahn was planned for the aftermath of an Axis victory over the Soviet Union, for a Greater Germany which would have spanned most of continental Europe. The cars were to be double-decker leviathans, 135 feet long and 22 feet tall, traveling at 150 mph, and kitted out with proper restaurants, cinemas, saloons and bars.

Period drawings show spacious, decadent luxury—and it is rather ironic that the Breitspurbahn’s only equivalent in mass transit, the Airbus A380 in various configurations, was built by, well, the French.